Molan A L, Meagher L P, Spencer P A, Sivakumaran S
Nutrition and Behaviour, AgResearch Ltd., Grasslands Research Centre, Private Bag 11008, Palmerston North, New Zealand.
Int J Parasitol. 2003 Dec;33(14):1691-8. doi: 10.1016/s0020-7519(03)00207-8.
The effects of flavan-3-ols (the monomer units of condensed tannins (CT)) and their galloyl derivatives on the viability of eggs, the development of first stage (L1) larvae, and the viability of the infective larvae of Trichostrongylus colubriformis were investigated under in vitro conditions. Each of the flavan-3-ol gallates showed some inhibition of egg hatching at 100 microg/ml, and 100% inhibition at 1000 microg/ml, with epigallocatechin gallate being the most effective in the egg hatch (EH) assay. In contrast, none of the flavan-3-ols were able to completely inhibit egg hatching. The flavan-3-ols and galloyl derivatives dose-dependently inhibited the development of infective larvae as assessed by the larval development (LD) assay. A larval migration inhibition (LMI) assay was used to assess the effect of flavan-3-ols and their galloyl derivatives on the motility of the infective third-stage (L3) larvae of T. colubriformis. In general, the flavan-3-ol gallates were more effective than the flavan-3-ols at immobilising the infective larvae as evidenced by their ability to inhibit more (P<0.05-0.01) larvae from passing through the LMI sieves. At 500 microg/ml, epigallocatechin gallate inhibited significantly more (P<0.1) larvae from passing through the sieves than did catechin gallate, epicatechin gallate, or gallocatechin gallate. Comparisons were made between the flavan-3-ols and their galloyl derivatives with the in vitro effects of CT extracts from several forage legumes, which have exhibited effects on parasites in vivo. The forage legumes tested at 200-500 microg/ml reduced the proportion of eggs that hatch, with comparable results to those obtained using the flavan-3-ols. The activities may be influenced by the prodelphinidin: procyanidin (PD:PC) ratios: CT extracts from Lotus pendunculatus and sainfoin have PD:PC ratios of 70:30 and 77:23, respectively, whereas the less active CT extract from Lotus corniculatus has a PD:PC ratio of 27:73. The active CT extracts from forage legumes have epigallocatechin as the dominant flavan-3-ol extender unit, and epigallocatechin is the most active flavan-3-ol in both the EH and LD assays.
在体外条件下，研究了黄烷-3-醇（缩合单宁（CT）的单体单元）及其没食子酰衍生物对蛇形毛圆线虫卵的活力、第一期（L1）幼虫的发育以及感染性幼虫活力的影响。每种黄烷-3-醇没食子酸盐在100微克/毫升时对卵孵化均有一定抑制作用，在1000微克/毫升时抑制率达100%，其中表没食子儿茶素没食子酸酯在卵孵化（EH）试验中效果最为显著。相比之下，黄烷-3-醇均不能完全抑制卵孵化。通过幼虫发育（LD）试验评估，黄烷-3-醇及其没食子酰衍生物对感染性幼虫的发育具有剂量依赖性抑制作用。采用幼虫迁移抑制（LMI）试验评估黄烷-3-醇及其没食子酰衍生物对蛇形毛圆线虫感染性第三期（L3）幼虫运动能力的影响。总体而言，黄烷-3-醇没食子酸盐在固定感染性幼虫方面比黄烷-3-醇更有效，这体现在它们能够抑制更多（P<0.05 - 0.01）的幼虫穿过LMI筛网。在500微克/毫升时，表没食子儿茶素没食子酸酯抑制穿过筛网的幼虫数量显著多于（P<0.1）儿茶素没食子酸酯、表儿茶素没食子酸酯或没食子儿茶素没食子酸酯。对黄烷-3-醇及其没食子酰衍生物与几种豆科牧草CT提取物的体外效应进行了比较，这些豆科牧草CT提取物在体内已显示出对寄生虫的作用。测试的豆科牧草在200 - 500微克/毫升时可降低孵化卵的比例，其结果与使用黄烷-3-醇获得的结果相当。这些活性可能受原花青定：原花青素（PD：PC）比例的影响：百脉根和红豆草的CT提取物的PD：PC比例分别为70：30和77：23，而活性较低的牛角花CT提取物的PD：PC比例为27：73。豆科牧草的活性CT提取物以表没食子儿茶素作为主要的黄烷-3-醇延伸单元，并且表没食子儿茶素在EH和LD试验中都是活性最高的黄烷-3-醇。
